全文获取类型
收费全文 | 2050篇 |
免费 | 155篇 |
专业分类
2205篇 |
出版年
2022年 | 10篇 |
2021年 | 26篇 |
2019年 | 22篇 |
2018年 | 21篇 |
2017年 | 18篇 |
2016年 | 27篇 |
2015年 | 56篇 |
2014年 | 83篇 |
2013年 | 89篇 |
2012年 | 97篇 |
2011年 | 88篇 |
2010年 | 43篇 |
2009年 | 67篇 |
2008年 | 75篇 |
2007年 | 97篇 |
2006年 | 80篇 |
2005年 | 81篇 |
2004年 | 82篇 |
2003年 | 62篇 |
2002年 | 55篇 |
2001年 | 67篇 |
2000年 | 71篇 |
1999年 | 59篇 |
1998年 | 47篇 |
1997年 | 44篇 |
1996年 | 34篇 |
1995年 | 37篇 |
1994年 | 23篇 |
1993年 | 34篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 33篇 |
1989年 | 36篇 |
1988年 | 39篇 |
1987年 | 37篇 |
1986年 | 47篇 |
1985年 | 32篇 |
1984年 | 33篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 37篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 26篇 |
1975年 | 21篇 |
1974年 | 28篇 |
1973年 | 17篇 |
1972年 | 8篇 |
排序方式: 共有2205条查询结果,搜索用时 0 毫秒
61.
Petter Larsson 《Hydrobiologia》1991,225(1):281-290
Natural clones and clones from laboratory crossings of Daphnia pulex have been tested in their response to stimuli for male and ephippia formation. The clones are from ponds in Illinois, USA, an area with both obligate and cyclical clones of D. pulex. The progeny from two types of crosses were studied: 1) crosses between an obligate clone producing males and a cyclical clone producing only females, and 2) self-fertilization within a cyclical clone producing both sexes. Both the natural and the artificial clones showed great variation in response to environmental stimuli for males. Ephippia response seems more equal among the clones, but two of the artificial clones could hardly be stimulated to produce ephippia in the induction experiments. In crowded cultures, however, they produced a few. Crossings between cyclicals and obligates yielded mostly cyclical progeny. Progeny from the selfed clone had low survival and fecundity. 相似文献
62.
Secondary alcohols of Mycobacterium xenopi were studied by gas chromatography and gas chromatography-mass spectrometry. Mycobacterial cells were hydrolysed and the liberated alcohols separated by extraction and analysed both underivatized and as trimethylsilyl, methyl ether- and pentafluorobenzoyl derivatives. Seven straight-chain secondary alcohols containing from 18 to 24 carbon atoms and two branched-chain secondary alcohols with 21 and 23 carbon atoms were present in all of the studied strains. 相似文献
63.
64.
65.
Gas chromatography/mass spectrometry was used to detect the presence of Enterobacter cloacae in cultures of Leuconostoc mesenteroides, an organism used in an industrial process for production of dextrane. The penta-fluorobenzoyl-methyl ester derivative of 3-hydroxy-myristic acid, a characteristic compound of gram-negative bacteria, was used as the analyte. By using gas chromatography/mass spectrometry with selected ion monitoring, E. cloacae was determined over the range of 1 ppm to 1% in cultures of L. mesenteroides. The proposed analytical approach represents a useful alternative to conventional methods for determining contaminating organisms in industrial fermentation processes. 相似文献
66.
Muscle hypertrophy in bodybuilders 总被引:4,自引:0,他引:4
P A Tesch L Larsson 《European journal of applied physiology and occupational physiology》1982,49(3):301-306
Muscle biopsy samples were obtained from m. vastus lateralis and m. deltoideus of three high caliber bodybuilders. Tissue specimens were analysed with respect to relative distribution of fast twitch (FT) and slow twitch (ST) fiber types and different indices of fiber area. In comparison to a reference group of competitive power/weight-lifters the following tendencies were observed: the percentage of FT fibers was less, mean fiber area was smaller and selective FT fiber hypertrophy was not evident. Values for fiber type composition and fiber size were more similar to values reported for physical education students and non-strength trained individuals. The results suggest that weight training induced muscle hypertrophy may be regulated by different mechanisms depending upon the volume and intensity of exercise. 相似文献
67.
Serum ionized calcium concentrations (CaF) were determined in 87 Swedish red-and-white cows and 10 Swedish Friesian cows with clinical signs of parturient paresis. All cows were in the week prior to or after parturition. A classification of the severity of hypocalcemia in terms of serum ionized calcium was devised. Eight cows had normal serum ionized calcium concentrations (Cap 1.06–1.26 mmol/1); 15 had slight (CaF 0.80–1.05 mmol/1); 43 a moderate (CaF 0.50–0.79 mmol/1), and 31 asevere (CaF < 0.50 mmol/1) hypocalcemia. All cows were given 8 or 8.3 g of calcium intravenously. Of 8 normocalcemic cows 7 (87.5 %) reached a maximum posttreatment serum ionized calcium concentration > 1.80 mmol/1 (severe hypercalcemia). This was also found in 13 of 15 (86.7 %) slightly hypocalcemic cows and in 31 of 43 (72.1 %) moderately hypocalcemic cows. In the severe hypocalcemia group 14 of 31 (45.2 %) had maximum posttreatment Cap > 1.80 mmol/1). These findings emphazise the need of a rapid pretreatment evaluation of the degree of hypocalcemia. The present study also underlined the difficulty in predicting serum ionized calcium from serum total calcium concentrations. 相似文献
68.
Anders
lund Hans Kindahl Ernst Oliw ke Lindgren Jan Bertil Larsson 《Prostaglandins & other lipid mediators》1980,19(5):791-803
Abortion or delivery were induced by extra-amniotic instillation of Rivanol during the second trimester in twelve patients and during the third trimester in two patients with fetal death and one patient with fetal acrania. Serial sampling of amniotic fluid was performed through a transabdominal catheter and the levels of free arachidonic acid (AA), prostaglandin F2α (PGF2α), prostaglandin E2 (PGE2), 6-keto-prostaglandin F1α (6-keto-PGF1α) and thromboxane B2 (TXB2) were determined. The levels of AA, PGF2α, PGE2, 6-keto-PGF1α and TXB2 in amniotic fluid increased significantly during induction with the exception of AA in fetal death which was high and remained constant during induction. Furthermore, PGF2α, 6-keto-PGF1α and TXB2 were all significantly correlated to AA.These observations suggested that free AA is released during Rivanol-induction of abortion and labour giving an increased synthesis of PGF2α, PGE2 prostacyclin and thromboxane A2 in the fetal membranes and the decidua but not in the fetus. This increase might be relevant for the initiation and progress of abortion and labour in these patients. 相似文献
69.
Bo Mattiasson Per-Olof Larsson Lennarth Lindahl Peter Sahlin 《Enzyme and microbial technology》1982,4(3):153-157
A vitamin B1 (thiamin)-sensitive electrode has been devised by combining an oxygen electrode with a yeast-containing membrane. The assembly was used for assaying thiamin at concentrations down to 10?11 gl?1. The analytical procedure developed should allow the measurement of 10–20 samples per hour. The performance of the yeast electrode was improved when alginate membranes reinforced with a nylon network were used. An apparatus for preparing such membranes is described together with a magnetic membrane holder facilitating handling of membranes in combination with electrodes. 相似文献
70.
Prostaglandin involvement in contractions evoked in rabbit detrusor by field stimulation and by adenosine 5'-triphosphate 总被引:1,自引:0,他引:1
Previous reports suggest that in rabbit urinary bladder both noncholinergic nonadrenergic excitatory responses and the contraction produced by adenosine 5'-triphosphate (ATP) are antagonized by indomethacin. We have attempted by further indirect testing on isolated detrusor strips to determine what role prostaglandins (PGs) might play in these processes. The second part of the biphasic contractile response to ATP was reduced to about 30% of control by PG synthesis inhibitors but the initial phase of the ATP response and te contraction produced by the beta, gamma-methylene analogue of ATP were unaffected. At concentrations that did not affect the response to acetylcholine but greatly suppressed the response to arachidonic acid, indomethacin antagonized the contraction evoked by field stimulation by about 30% at 1-2 Hz (largely noncholinergic and nonadrenergic). SC 19220, a putative PG receptor blocker, also produced about 25% reduction in the response to field stimulation but with only about 50% reduction in the response to arachidonic acid, PGE2, or PGF2alpha, SC 19220 also antagonized the frequency-response curve in atropine-treated strips. These findings lead us to suggest that beside maintaining tone and spontaneous activity in the bladder PGs mediate the slow tonic phase of the ATP response and may contribute to facilitatory modulation of noncholinergic nonadrenergic excitatory transmission. 相似文献